As is well-known, electrochemical plants comprise a multiplicity of electrolyzers, each one consisting in a plurality of elementary cells assembled in the so-called filter press arrangement, said elementary cells being electrically connected either in series (bipolar electrolyzers) or in parallel (monopolar electrolyzers). The electrolyzers are usually fed with a current up to 500 kA and a maximum voltage of 10 V in the case of monopolar electrolyzers, and with a current up to 20 kA and a maximum voltage of 300 Volts, in the case of bipolar electrolyzers.
In standard operating conditions, when one of the electrolyzers is to be serviced, the electrolysis current fed to the whole plant has to be interrupted to permit maintenance or substitution of the electrolyzer to be serviced.
A prolonged interruption of current to the whole plant (electrolysis circuit) causes not only a production loss but also possible damages to the internal components of the electrolyzers due to the remarkable shifts of temperature and pressure. In addition, with a prolonged interruption of current also auxiliary equipment of the plant, such as compressors, could be damaged. To avoid such a problem, the shut down as well as start-up operations require a substantial amount of time, as the current has to be respectively decreased or increased by small steps. The clear consequence of this is a further loss of production.
In conventional plants, this problem is overcome by resorting to a jumper switch means providing for by-passing the electrolyzer to be serviced in the electrical circuit of the multiplicity of electrolyzers. To avoid interruption of the electrolysis process in the remaining electrolyzers, the by-pass (disconnection) and the connection of the electrolyzer, once serviced, takes place under electric current load.
The electrolyzer to be serviced may by-passed by utilizing copper bus-bars which are connected to the terminal contacts of the electrolyzer. As the current travelling across the plant is extremely high, the operation of connecting the bus-bars involves severe dangers.
To overcome this problem, the short-circuiting bus-bars are provided with stationary contacts as well as mobile contacts, sliding over the stationary ones, which permits a full and safe operation. Further, the mobile contacts offer other advantages over the stationary ones, that is stability in the presence of vibrations, complete absorption of the thermal expansions, single contact series resistance.
The contact pressure is ensured by suitable springs, one for each mobile contact. This arrangement of bus-bars, fixed and mobile contacts, is provided by those equipments, known in the technical field as jumper switches.
However, due to the high operating current, also onto the mobile contacts arcing may take place during short-circuiting of the electrolyzers.
This problem is overcome by suitable arcing-protecting contacts which provide for anticipated closing and deferred opening with respect to the main contacts, either mobile or stationary, in order to avoid any arcing to the latter.
For switches operating with currents up to 20 kA and voltages up to 300 Volts, in addition to the arcing-protecting contacts, also a sacrificial fuse is provided.
These jumper switches, although sufficiently widespread, require a remarkable maintenance. The arcing-protecting contacts must be substituted usually every some tens of opening and closing procedures, and the sacrificial fuse after each operation. The substitution of the arcing-protecting contacts and sacrificial fuse not only is extremely expensive, but requires also the assistance of specialized maintenance personnel. Further, the risk of arcing in the contacts is not completely eliminated by the above solutions. In fact, the electric current is often decreased before proceeding to the short-circuit operation. In addition, forgetting to substitute the fuse cause serious danger during the next short-circuit operation.